The invention relates to a magnetic brush developing process for use in the electrophotographic and electrostatic recording techniques.
The magnetic brush developing process represents one of the dry type developing processes, and employs a sleeve of a non-magnetic material, having substantially the same width as a photosensitive member or a recording paper (hereinafter referred to as a record member), in combination with a magnet received inside the sleeve and extending the full width thereof. Either the sleeve or the magnet is caused to rotate or both may be rotated in opposite directions to convey a magnetic brush, formed by a quantity of the developer which is attracted onto the surface of the sleeve, about the sleeve axis. At a given developing position, the magnetic brush formed is brought into contact with an electrostatic latent image on the record member for converting it into a visual image.
The developer used in the magnetic brush developing process may be either a two component developer, involving the use of a carrier, or a single component developer which does not require a carrier. A two component developer comprises a mixture of toner particles formed by resins and carbons and a carrier formed by iron powder or magnetic powder. By agitation, both components are triboelectrically charged, so that they bear an electric charge of opposite polarities. An electrostatic latent image having an increased proportion of thin lines or having a reduced surface potential can be satisfactorily developed by a suitable choice of the toner and carrier materials in the triboelectricity series depending on the polarity of the latent image. However, it suffers from a poor durability which results from wear of the developer because of repeated triboelectric charging. In addition, there must be provided some means for maintaining a constant toner concentration since toner alone is subject to dissipation in developing the image.
On the other hand, the single component developer comprises iron or other magnetic powder and carbon which are bonded together with a binder into the form of particles, and is sometimes referred to as a magnetic toner. Because there is no carrier, the toner cannot be charged without a special means. In addition, since the developing is achieved by the electrostatic induction or polarization due to the static electricity of the latent image, there result difficulties that a latent image having an increased proportion of thin lines or having a reduced surface potential cannot be developed in a satisfactory manner and that the resulting image lacks sharpness.